WO2015108036A1 - Method for producing stretched film - Google Patents

Abstract

This method for producing a stretched film has a step for forming a pre-stretching film (100) by using rollers (230, 240) to cool/solidify a thermoplastic resin melt-extruded from molding dies (220), and a step for forming a stretched film by heating/stretching the pre-stretching film (100) in at least one direction, and the method is characterized in that in the step for forming the pre-stretching film (100), the pre-stretching film (100) is formed in a manner such that the center of the pre-stretching film (100) contracts by means of planar stretching and the two edges contract by means of single-axis stretching, and so if the minimum thickness of the boundary formed between the center and the two edges is t_b and the average thickness of the center is t_c, the ratio (t_b/t_c) of the minimum thickness t_b and the average thickness t_c is at least 0.75.

Description

Method for producing stretched film

The present invention relates to a method for producing a stretched film.

When producing a stretched film, a method of preparing a film as a material and stretching the prepared film is used. As a method of stretching the film, the film is held in a heating furnace while holding both ends of the film with clips. There is known a simultaneous biaxial stretching method in which heating and stretching are simultaneously performed in the length direction and the width direction by clips that are conveyed and gripped at both ends of the film in a heating furnace.

In such a simultaneous biaxial stretching method, in the heating furnace, the film is stretched by heating to the necessary stretching ratio by pulling the film in the length direction and the width direction. In addition, a large stress is applied to both ends of the film, which is the part gripped by the clip, resulting in tears at both ends of the film and where the thickness of the film is thin. It may break.

On the other hand, for example, in Patent Document 1, in order to prevent breakage of the film at the time of heat stretching by simultaneous biaxial stretching, both ends held by the clips are made thicker than the center portion of the film before heat stretching. Thus, a technique for reinforcing is disclosed.

JP-A-11-105131

However, in the technique of Patent Document 1 above, the film for heat stretching is formed by melt extrusion of a thermoplastic resin with a molding die, so that the thickness of a part of the film is reduced during melt extrusion. Therefore, there is a problem that the thinned portion is torn when the heat stretching is performed and the entire film is broken.

That is, in a thermoplastic resin film melt-extruded from a molding die, it is called neck-in that extends in the length direction and narrows the film width after being melt-extruded and taken up by a cooling roll or the like. The phenomenon occurs. Such neck-in is considered to occur as follows. That is, the thermoplastic resin melt-extruded from the molding die has a thermoplastic resin adjacent to each other at the center in the width direction of the film, so that the flow direction of the thermoplastic resin is limited, Plane extension is performed along a predetermined surface inside the thermoplastic resin, whereby shrinkage in the width direction is suppressed, and shrinkage is mainly performed in the thickness direction. On the other hand, the thermoplastic resin melt-extruded from the forming die has no thermoplastic resin adjacent to the outer side surface at the portion that becomes both ends in the width direction of the film, so that the thermoplastic resin flows freely. Then, it extends uniaxially around a predetermined axis inside the thermoplastic resin, and thereby contracts in the width direction in addition to the thickness direction. Therefore, in the formed film, the boundary part between the width direction center part and the width direction both ends will be dented in the thickness direction by the difference in the shrinkage | contraction form of a thermoplastic resin, and thickness will become thin. And when such a film is heat-stretched, there is a problem that cracks are generated at the thin boundary portion, which makes it easy to break the entire film.

The present invention has been made in view of such a situation, and in producing a stretched film by heating and stretching the film, it is possible to prevent the film from being broken, and to provide a stretched film excellent in productivity and quality. It aims at providing the manufacturing method of the stretched film which can be obtained.

By adjusting the thickness of the boundary portion formed between the central portion and both end portions of the film with respect to the average thickness of the central portion of the film, the present inventors can The inventors have found that the object can be achieved and have completed the present invention.

That is, according to the present invention, after the thermoplastic resin is melt-extruded from a molding die, it is cooled by a roll and solidified to form a pre-stretch film forming step, and the pre-stretch film forming step. A stretched step of forming a stretched film by heat-stretching the film in at least one direction, wherein in the pre-stretch film forming step, the central portion of the unstretched film is By stretching in a plane extending along a specific surface located near the central position in the thickness direction of the film before stretching or near the central position, both ends of the film before stretching are contracted toward the specific surface, By uniaxial extension that extends around a specific axis that passes through the center of the both ends or near the center position, it contracts around the specific axis. In, a minimum thickness of the boundary portion formed between said central portion and the both end portions and t _b, the average thickness of the central portion in the case of the t _c, the minimized thickness t _b of the boundary There is provided a method for producing a stretched film, wherein the pre-stretch film is formed so that the ratio “t _b / t _c ” to the average thickness t _c of the central portion is 0.75 or more. .

In the production method of the present invention, an acrylic resin is preferably used as the thermoplastic resin.
In the production method of the present invention, as the thermoplastic resin, a first thermoplastic resin that forms an inner region located on the inner side in the width direction of the film before stretching, and an outer region located on the outer side in the width direction of the film before stretching. It is preferable to use a second thermoplastic resin different from the first thermoplastic resin.
In the production method of the present invention, an acrylic resin is preferably used as the first thermoplastic resin.
In the manufacturing method of this invention, it is preferable to use the mixed resin formed by mix | blending the thermoplastic resin which has a glass transition temperature lower than the said acrylic resin with a polycarbonate (PC) as said 2nd thermoplastic resin.
In the production method of the present invention, it is preferable to use a thermoplastic resin having a glass transition temperature difference of 10 ° C. or less as the first thermoplastic resin and the second thermoplastic resin.
In the production method of the present invention, the maximum thickness of the end portions in the case of a t _e, the ratio "t _{e /} t _c" between the maximum thickness t _e of the end portions and the average thickness t _c of the central portion, It is preferable to form the pre-stretch film in the pre-stretch film forming step so as to be in the range of 1.0 to 2.0.
In the production method of the present invention, wherein when the slit width of the outlet of the molding die was t _s, the ratio "t _s and the average thickness t _c of the slit width t _s and the central portion of the outlet of the molding die It is preferable to form the pre-stretch film in the pre-stretch film forming step so that “/ t _c ” is 8.0 or less.
In the production method of the present invention, it is preferable that the heat stretching of the pre-stretched film in the stretching step is performed by simultaneous biaxial stretching that simultaneously stretches in the length direction and the width direction of the pre-stretched film.
In the manufacturing method of this invention, it is preferable that the draw ratio with respect to the extending | stretching direction of the heat stretching of the said film before extending | stretching in the said extending process shall be 3 times or less.
In the production method of the present invention, it is preferable that the heat stretching of the pre-stretched film in the stretching step is performed so that the thickness of the central portion of the stretched film after the heat stretching is in the range of 15 to 50 μm.
Moreover, in the manufacturing method of this invention, it is preferable to have the smoothing process of smoothing the both side surfaces which prescribe | regulate the thickness of the said film before extending | stretching before the said extending process.
Furthermore, it is preferable that the manufacturing method of this invention performs the smoothing in the said smoothing process by removing the area | region located in the both ends of the width direction of the said film before extending | stretching.

According to the present invention, when producing a stretched film by heat-stretching the film, a stretched film production method capable of appropriately performing heat-stretching and obtaining a stretched film excellent in productivity and quality is provided. Can be provided.

FIG. 1 is a diagram for explaining a method of producing a pre-stretch film. FIG. 2 is a view for explaining neck-in of a melt-extruded thermoplastic resin. FIG. 3 is a view for explaining shrinkage of the melt-extruded thermoplastic resin. FIG. 4 is a diagram illustrating an example of the thickness of the unstretched film with respect to the position in the width direction. FIG. 5 is a diagram for explaining a method of stretching a pre-stretched film by a simultaneous biaxial stretching method in a stretching step. FIG. 6 is a graph showing the results of measuring the thickness of the pre-stretched film and stretched film produced in Examples and Comparative Examples with respect to the width direction position. FIG. 7 is a diagram for explaining a method of producing a pre-stretch film (composite film) made of the first thermoplastic resin and the second thermoplastic resin. FIG. 8 is a diagram for explaining neck-in of a thermoplastic resin melt-extruded when a composite film is manufactured. FIG. 9 is a diagram for explaining an example of a thermoplastic resin that shrinks immediately after being melt-extruded when a composite film is manufactured. FIG. 10 is a diagram illustrating an example of the thickness of the composite film with respect to the position in the width direction. FIG. 11 is a diagram for explaining a method of stretching a composite film by a simultaneous biaxial stretching method in a stretching step. FIG. 12 is a graph showing the glass transition temperature of a mixed resin obtained by blending polyethylene terephthalate (PET) with polycarbonate (PC). FIG. 13 is a diagram for explaining another example of a composite film that shrinks immediately after being melt-extruded. FIG. 14 is a graph showing the results of measuring the thickness of the composite films and stretched films produced in Examples and Comparative Examples with respect to the width direction position.

<< first embodiment >>
Hereinafter, a first embodiment of the present invention will be described based on the drawings.
The method for producing a stretched film according to the first embodiment includes a pre-stretch film forming step of forming a pre-stretch film by melt-extruding a thermoplastic resin with a molding T-die, and the pre-stretch film in the length direction. And a stretching step of heating and stretching in the width direction.

<Film forming step before stretching>
The pre-stretching film forming step is a step of obtaining the pre-stretching film 100 by melt-extruding a thermoplastic resin from a T die. Here, FIG. 1 is a figure for demonstrating the film formation process before extending | stretching.

In the pre-stretching film forming step, first, the thermoplastic resin is supplied to the T dice 220 through the feed block 210 in a state of being melted by heating.

In the present embodiment, the feed block 210 is connected to a melt extruder (not shown) for melt-extruding a thermoplastic resin. The melt extruder is not particularly limited, and either a single screw extruder or a twin screw extruder can be used. In this embodiment, the thermoplastic resin is supplied to the feed block 210 by being melt-extruded at a temperature equal to or higher than the melting point (melting) temperature by a melt extruder.

In the present embodiment, the thermoplastic resin may be selected according to the intended use of the stretched film. For example, acrylic resin (PMMA), cyclic olefin copolymer (COC), polycarbonate (PC), One type of polyester terephthalate (PET) or the like can be used alone, or a mixed resin in which two or more types are mixed can be used.

In the T die 220, the thermoplastic resin supplied from the feed block 210 is widened in the width direction by the manifold 221 provided in the T die 220, and is thereby extruded from the die slip 222 into a sheet shape.

Next, as shown in FIG. 1, the extruded sheet-like thermoplastic resin is continuously taken up by the touch roll 230 and the cooling roll 240, and sandwiched and cooled to be solidified to obtain the unstretched film 100.

And in this embodiment, the produced film 100 before extending | stretching is wound up by the film winding roll (not shown) before extending | stretching, and, thereby, the film 100 before extending | stretching can be obtained continuously. .

In the pre-stretched film 100 obtained in this way, a phenomenon called neck-in that shrinks in the width direction after being melt-extruded from the die slip 222 of the T-die 220 and taken up by the cooling roll 240 is present. appear.

Here, FIG. 2 is a view showing a cross section of the die slip 222 of the T-die 220 and the pre-stretching film 100 formed in the present embodiment. The relationship with the width of the film 100 is shown. In the present embodiment, when the pre-stretch film 100 is formed, the thermoplastic resin is melt-extruded by the width of the die slip 222 by the T-die 220, but after being melt-extruded until taken up by the cooling roll 240. In the meantime, as indicated by the arrows shown in FIG. 2, neck-in that shrinks in the width direction occurs, and the width of the resulting unstretched film 100 becomes smaller than the width dimension of the die slip 222.

In such a neck-in, the thermoplastic resin melt-extruded from the T-die 220 contracts in the direction of the arrow shown in FIG. 2, that is, the direction at which the center of the unstretched film 100 is indicated by the arrow ( It is generated by contracting in the direction (thickness direction and width direction) indicated by the arrows. Then, the thermoplastic resin melt-extruded from the T-die 220 contracts by neck-in so that the cross-sectional shape becomes as shown in FIG.

Here, FIG. 3 is a diagram for explaining the shrinkage of the melt-extruded thermoplastic resin. In the present embodiment, the thermoplastic resin melt-extruded from the T-die 220 is, as shown in FIG. 3, the thermoplastic resin due to the presence of the adjacent thermoplastic resin in the portion that becomes the central portion 110 of the unstretched film 100. Thus, the thermoplastic resin contracts in the thickness direction as indicated by the arrows due to the planar extension extending along the surface α located at or near the center in the thickness direction. On the other hand, the thermoplastic resin melt-extruded from the T-die 220 has a thermoplastic resin adjacent to the outer side surfaces of both end portions 120 at the portions to be the both end portions 120 of the unstretched film 100 as shown in FIG. Since the thermoplastic resin does not exist, the thermoplastic resin flows relatively freely. As a result, the uniaxial extension extending about the axis β passing through the center of the both ends 120 or near the center position causes the width in addition to the thickness direction as shown by the arrows. It also shrinks in the direction. Thereby, between the center part 110 and the both ends 120, the boundary part 130 of the shape dented in the thickness direction is formed by the difference in the shrinkage | contraction form of a thermoplastic resin.

Therefore, in the pre-stretch film 100 formed by the method shown in FIG. 1, the boundary portion 130 between the central portion 110 and both end portions 120 is particularly thin as shown in FIG. In addition, FIG. 4 is a figure which shows an example of the result of having measured the thickness with respect to the position of the width direction about the film 100 before extending | stretching.

Here, when the thickness of the boundary portion 130 of the formed pre-stretching film 100 is too thin with respect to the thickness of the central portion 110, the boundary where the thickness is thin when the pre-stretching film 100 is heat stretched in the stretching step. There is a problem that cracks are likely to occur in the portion 130 and heating and stretching cannot be performed appropriately.

On the other hand, in this embodiment, as shown in FIG. 4, the average thickness of the central portion 110 is set to t _c for the unstretched film 100 formed by melt extrusion using a T-die 220 and drawing by a cooling roll 240. When the minimum thickness of the boundary 130 is t _b , the ratio of these thicknesses “t _b / t _c ” is adjusted to 0.75 or more to heat the unstretched film 100 as will be described later. When stretching, the boundary 130 can be effectively prevented from cracking, and the productivity of the stretched film can be improved.

Note that the average thickness t _c of the central portion 110 shown in FIG. 4 is an average value of the thickness of the portion where the thickness of the central portion 110 is stable. For example, the thickness is ± 5 with respect to the center of the central portion 110. It can be an average value of thickness in a region within ˜10%. As the minimum thickness t _b of the boundary portion 130, of the two minimum thickness of the boundary portion 130 of the pre-stretch film 100, a more thinner thickness.

<Extension process>
The stretching step is a step of heating and stretching the pre-stretching film 100 obtained by the pre-stretching film forming step in the length direction and the width direction. Here, FIG. 5 is a figure for demonstrating an extending process. In the present embodiment, in the stretching step, the unstretched film 100 is sent out from the above-described unstretched film winding roll, and the length direction and the width direction are held while the unstretched film 100 is held by the clip 310 as shown in FIG. The film 100 before stretching is heated and stretched by a simultaneous biaxial stretching method in which the film is stretched simultaneously.

Specifically, in the stretching step, the unstretched film 100 is continuously fed out from the unstretched film winding roll, the unstretched film 100 is gripped at regular intervals using a plurality of clips, and each of the clips 310 is stretched before stretching. The film 100 is transported into the stretching furnace 320, and in the stretching furnace 320, the pre-stretching film 100 is pulled in the length direction and the width direction by each clip 310 to be stretched. At this time, the unstretched film 100 is transported while being held by the clip 310, so that it passes through the stretching furnace 320, and is stretched in the pre-tropical zone in the stretching furnace 320. The pre-film 100 is preheated to a temperature that is about 10 to 30 ° C. higher than the glass transition temperature of the thermoplastic resin that constitutes the film, and is then kept in the drawing zone in the drawing furnace 320 by the clip 310 while keeping the heat. It is pulled in the length direction and the width direction and stretched in the length direction and the width direction. And a stretched film can be obtained by cooling and solidifying in the cooling heat fixed zone following this. And the stretched film can be obtained continuously by opening the clip 310 and winding up with a roll.

In the present embodiment, a pair of guide rails for moving the clip 310 so as to pass through the drawing furnace 320 is provided. The pair of guide rails are respectively installed at the position of the clip 310 that holds the upper side of the pre-stretching film 100 shown in FIG. 5 and the position of the clip 310 that holds the lower side. They are parallel, separated from each other in the width direction of the pre-stretching film 100 in the stretching band, and parallel to each other in the cooling heat fixing band. Alternatively, in the cooling heat fixing band, the distance between the pair of guide rails in the cooling heat fixing band is determined in consideration of the shrinkage when the stretched film heated and stretched in the stretching band is solidified. On the basis of the width of the stretched film on the side, it may be approximated by several percent in the width direction. In the present embodiment, the clip 310 that holds the unstretched film 100 moves along such a guide rail so that the unstretched film 100 can be conveyed and stretched.

In this embodiment, the pre-stretching film 100 is stretched in the stretching zone in the stretching furnace 320 using the clip 310 that moves along such a guide rail. That is, in the stretching zone in the stretching furnace 320, the clip 310 that holds the unstretched film 100 is moved so as to spread in the width direction along the guide rail, and at the same time, the interval between the clips 310 is increased. Thus, the unstretched film 100 is pulled in the length direction and the width direction as indicated by arrows in FIG. Thereby, the film 100 before extending | stretching is heat-stretched until it becomes a draw ratio required in the length direction and the width direction. And the film 100 before extending | stretching is heat-stretched, Then, it is cooled and solidified in the cooling heat fixing zone in the stretching furnace 320, and is wound up by a roll installed outside the stretching furnace 320. Thus, a stretched film can be obtained continuously.

In this embodiment, it is possible to obtain a stretched film by making the stretching step and the pre-stretching film forming step into a continuous line (step).

In this embodiment, when the pre-stretch film 100 is stretched by heating, the stretch ratio with respect to the stretching direction is preferably within 3 times, more preferably within 2.5 times, and even more preferably within 2 times. . Thereby, the fracture | rupture of the film 100 before extending | stretching during heat-stretching can be prevented more effectively, and the heat-stretching of the film 100 before extending | stretching can be performed appropriately.

In this embodiment, the stretched film obtained by heating and stretching the pre-stretched film 100 has a thickness of the central portion 110 of preferably 15 to 50 μm, more preferably 20 to 40 μm. By controlling the thickness of the central portion 110 in the stretched film within the above range, it is possible to more effectively prevent the pre-stretching film 100 from being broken during the heat stretching and appropriately heat-stretch the pre-stretching film 100. .

Furthermore, in the present embodiment, the stretched film obtained by heating and stretching the pre-stretched film 100 may be removed by cutting the both ends 120 as necessary. Thereby, the part of the both ends 120 with especially thick thickness in a stretched film can be removed, and the thickness of the whole stretched film can be equalize | homogenized.

As described above, in this embodiment, a stretched film is obtained by forming the unstretched film 100 made of a thermoplastic resin in the pre-stretching film forming step and heating and stretching the pre-stretched film 100 in the stretching step. be able to.

Here, in the present embodiment, when the pre-stretch film 100 is formed by the pre-stretch film forming step, the ratio “t _b ” between the average thickness t _c of the central portion 110 and the minimum thickness t _b of the boundary portion 130. The thickness of the unstretched film 100 is adjusted so that “/ t _c ” is 0.75 or more. Thereby, when heat-stretching the film 100 before extending | stretching at an extending | stretching process, generation | occurrence | production of the crack in the boundary part 130 with thin thickness can be prevented effectively, and productivity of a stretched film can be improved.

In addition, when the film 100 before extending | stretching is heat-stretched, the boundary part 130 among the films 100 before extending | stretching has a low extending | stretching stress required for extending | stretching by thinness, and will be extended preferentially. As the stretching proceeds at the boundary portion 130, the stretching stress at the boundary portion 130 gradually increases, and when the stretching stress necessary for stretching at the central portion 110 is reached, the central portion 110 is also stretched following the boundary portion 130. Become so. At this time, if the thickness of the boundary portion 130 is too thin with respect to the central portion 110, the boundary portion 130 breaks before the central portion 110 starts to be stretched while the boundary portion 130 is being stretched. End up. Further, if the thickness of the boundary portion 130 is too small with respect to the central portion 110, the impact when releasing the unstretched film 100 from the clip 310 and the obtained stretched film after heating and stretching as shown in FIG. Cracks are also generated in the boundary portion 130 due to the stress at the time of winding on the roll.

Here, conventionally, as a method for preventing breakage of the film during heat stretching by simultaneous biaxial stretching, a method of forming both end portions of the film before heat stretching thicker than the central portion is known. However, when the film to be stretched is produced by melt extrusion using the T-die 220, the boundary formed between the center portion and both end portions of the film even if both end portions of the film are thickened as described above. As shown in FIG. 3, the thickness of the portion is reduced, and there is a problem that a crack occurs at such a boundary portion when the film is heated and stretched.

On the other hand, according to the present embodiment, the average thickness t _c of the central portion 110 and the minimum of the boundary portion 130 of the unstretched film 100 formed by being melt-extruded by the T-die 220 and then pulled by the cooling roll 240. By adjusting the ratio “t _b / t _c ” to the thickness t _b within the above range, when the film 100 before stretching is heated and stretched, the occurrence of cracks at the boundary portion 130 can be effectively prevented, The productivity of the film can be improved.

In the present embodiment, the ratio “t _b / t _c ” between the average thickness t _c of the central portion 110 and the minimum thickness t _b of the boundary portion 130 may be 0.75 or more as described above. , Preferably 0.8 or more, more preferably 0.9 or more.

In the present embodiment, the ratio “t _b / t _c ” between the average thickness t _c of the central portion 110 and the minimum thickness t _b of the boundary portion 130 is adjusted to the above range for the pre-stretch film 100 to be formed. There are no particular restrictions on the method used, for example, a method using a resin having a lower extensional viscosity as the thermoplastic resin, a method of adjusting the slit width of the die slip 222 of the T die 220, and the method of using the T die 220 and the cooling roll 240. A method of reducing the distance, a method of reducing the take-up speed of the pre-stretching film 100 by the cooling roll 240, or the like can be used alone or in combination.

In this embodiment, among these methods, the type of applicable thermoplastic resin is not limited, and the slit width of the die slip 222 is adjusted from the viewpoint of not reducing the production efficiency of the pre-stretching film 100. It is preferable to use the method to do. At this time, when the slit width of the die lip 222 was _{t s,} the ratio _"t s / _{t c"} of the average thickness _{t c} of the slit width _{t s} and the central portion 110 of the die lip 222, preferably It adjusts so that it may be 8.0 or less, More preferably, it is 6.0 or less, More preferably, it is 5.0 or less. Thereby, the thickness of the unstretched film 100 obtained by melt extrusion with the T die 220 can be made more uniform, and the ratio “t _b ” between the average thickness t _c of the central portion 110 and the minimum thickness t _b of the boundary portion 130. / T _c ”can be appropriately adjusted to the above range.

In the present embodiment, the pre-stretched film 100 to be formed, the ratio _"t b / _{t c"} with minimum thickness _{t b} of the average thickness _{t c} and the boundary portion 130 of the central portion 110 as described above the In addition to adjusting to the range, by adjusting the maximum thickness of the both end portions 120 so as to be moderate, it is possible to more effectively prevent the pre-stretching film 100 from being broken during the heat stretching.

Specifically, in the case of forming the pre-stretch film 100, as shown in FIG. 4, the maximum thickness of the end portions 120 when the t _e, the average of the maximum thickness t _e and the central portion 110 of the end portions 120 The ratio “t _e / t _c ” with _respect to the thickness t _c is preferably adjusted to 1.0 to 3.0, more preferably 1.0 to 2.0, and still more preferably 1.0 to 1.5. Here, the maximum thickness t _e of the ends 120, of the thickness of the end portions 120 of the pre-stretched film 100 (the one end portion and another end portion in the width direction), and more thicker thickness. Incidentally, with respect to the average thickness _{t c} of the central portion 110, when the maximum thickness _{t e} of the end portions 120 is too thick, the unstretched film 100 obtained melt extrusion by a T die 220, the touch roll 230 and the chill roll When the two ends 120 are too thick when pinched by 240, the pressure concentrates on both ends 120 and the pressure is not uniformly transmitted to the entire unstretched film 100, and the thickness of the unstretched film 100 varies, and this is heated. The thickness of the stretched film obtained by stretching also tends to vary. On the other hand, with respect to the average thickness t _c of the central portion 110, when the maximum thickness t _e of the end portions 120 is too thin, the time of pre-stretched film 100 is melt extruded by T die 220 is neck-in at both ends 120 tends to increase the pulling force of the thermoplastic resin, whereby the thickness of the boundary portion 130 becomes thinner, and the pre-stretching film 100 is likely to break during the heat stretching.

In the present embodiment, it is preferable to smooth the side surfaces of both end portions 120 before heating and stretching the pre-stretch film 100 formed by the pre-stretch film forming step. By smoothing the side surfaces of both end portions 120 of the pre-stretching film 100, when the pre-stretching film 100 is heated and stretched by pulling the both end portions 120 of the pre-stretching film 100 in the stretching step, Concentration of local stress due to roughness can be prevented, generation of tears at both ends 120 can be prevented, and productivity of the stretched film can be improved.

The method for smoothing the side surfaces of both end portions 120 of the unstretched film 100 is not particularly limited, but a method of trimming a predetermined width from both side surfaces of both end portions 120 with a cutter, a method for polishing the end portions of both end portions 120, For example, a method of heat-pressing the end portions of the both end portions 120 can be used. The smoothing of the side surfaces of both end portions 120 reduces the unevenness of the side surfaces of both end portions 120, and when the pre-stretch film 100 is pulled in the length direction, stress is not concentrated on a part of both end portions 120. You can go to

When trimming the both ends 120 of the unstretched film 100 with a cutter, any cutter can be used as long as it can smoothly smooth the side surfaces of both ends 120 by trimming. You can use a rotary shear cutter that continuously rotates while rubbing the blade and lower blade and cut by shearing, or a laser cutter that uses a solid laser, semiconductor laser, liquid laser, gas laser, etc. From the viewpoint that the stress applied to the pre-stretching film 100 can be reduced and the occurrence of cracks in the pre-stretching film 100 during trimming can be prevented, a laser cutter is preferable.

In addition, when trimming both end portions 120 of the pre-stretched film 100, it is preferable to trim the both end portions 120 while heating. Thereby, the side surfaces of both end portions 120 can be made smoother, and breakage of the pre-stretching film 100 when the pre-stretching film 100 is heated and stretched can be more appropriately prevented.

Moreover, in the example mentioned above, as shown in FIG. 5, as a method of heating and stretching the pre-stretching film 100, a simultaneous biaxial stretching method in which the pre-stretching film 100 is heated and stretched in both the length direction and the width direction is used. Although the example used is shown, in this embodiment, you may use the method of uniaxially stretching the film 100 before extending | stretching only to a length direction.

In this case, the heat stretching in the length direction of the pre-stretching film 100 can be performed in the same manner as the simultaneous biaxial stretching method shown in FIG. That is, the film 100 before stretching is conveyed into the stretching furnace 320 while being gripped by the clip 310, and then heated and stretched only in the length direction by the clip 310 gripping the film 100 before stretching in the stretching furnace 320. Can be used.

In this embodiment, in both cases where simultaneous biaxial stretching is performed in the length direction and width direction, and when uniaxial stretching is performed only in the length direction, the unstretched film 100 is clipped 310 as shown in FIG. By stretching while gripping with, it is possible to improve the productivity of the stretched film compared to the conventional sequential biaxial stretching method, and the obtained stretched film has excellent quality can do.

Note that the conventional sequential biaxial stretching method is a method in which the pre-stretching film 100 produced by the method shown in FIG. 1 is first heat stretched in the length direction and then heat stretched in the width direction. In the sequential biaxial stretching method, the film 100 before stretching is heated and stretched in the length direction by being conveyed by a plurality of rolls, and then the width of the film 100 while being held by the clip 310 as shown in FIG. Heat stretch in the direction.

Here, the stretching in the length direction of the pre-stretching film 100 in the sequential biaxial stretching method is specifically performed as follows. That is, according to the sequential biaxial stretching method, the pre-stretching film 100 is preheated to the glass transition temperature of the thermoplastic resin constituting the pre-stretching film 100 while being transported by a plurality of preheated preheated rolls. The heated unstretched film 100 is continuously transported by a cooling roll while keeping heat by an infrared heater or the like. At this time, by making the conveyance speed by the cooling roll faster than the conveyance speed by the pre-tropical roll, a tension is generated between the pre-tropical roll and the cooling roll. Is stretched in the length direction to a necessary stretching ratio.

Here, in the sequential biaxial stretching method, when the pre-stretching film 100 is stretched in the length direction, the surface of the pre-stretching film 100 comes into contact with the preheating roll and the cooling roll. Scratches may occur on the surface, and the appearance quality of the obtained stretched film may be deteriorated. Further, in the sequential biaxial stretching method, when the film 100 before stretching is heated and stretched in the length direction, since the both ends 120 of the film 100 before stretching are not fixed with clips or the like, the film 100 before stretching is heated. There exists a possibility that it may shrink | contract in the width direction and productivity of a stretched film may fall.

On the other hand, according to this embodiment, the film 100 before stretching is stretched in the length direction by using the simultaneous biaxial stretching method described above or the method of uniaxial stretching only in the length direction described above. (That is, by using a method of stretching in the length direction while holding the pre-stretching film 100 with the clip 310 as shown in FIG. 5), it is possible to avoid contact with the roll. The stretched film obtained by heating and stretching the pre-stretched film 100 can improve the appearance quality by reducing the scratches on the surface, and is particularly suitable for use in optical films and the like that have strict requirements on the appearance quality. it can. Furthermore, according to this embodiment, since the film 100 before extending | stretching is hold | gripped with the clip 310 when extending | stretching the film 100 before extending | stretching to a length direction, about the film 100 before extending | stretching, the shrinkage | contraction of the width direction by a heat | fever is carried out. This can be prevented and the productivity of the stretched film can be improved.

<< Second Embodiment >>
Next, a second embodiment of the present invention will be described based on the drawings.
In the method for producing a stretched film according to the second embodiment, the first thermoplastic resin PA and the second thermoplastic resin PC different from the first thermoplastic resin are melt-coextruded by a molding T die. The film formation process before extending | stretching which forms the film (composite film) before extending | stretching by this, and the extending process which heat-extends this film before extending | stretching to a length direction and the width direction are provided.

<Film forming step before stretching>
The pre-stretching film forming step is a step of forming the pre-stretching film 100 by melt coextruding the first thermoplastic resin PA and the second thermoplastic resin PC from a T die. Here, FIG. 7 is a figure for demonstrating the film formation process before extending | stretching. In the present embodiment, as shown in FIG. 7, as the pre-stretch film 100, the first thermoplastic resin PA that forms an inner region located on the inner side in the width direction of the pre-stretch film 100, and the width of the pre-stretch film 100 A film made of the second thermoplastic resin PC forming the outer region located on the outer side in the direction is obtained. In the present embodiment, the inner region formed by the first thermoplastic resin PA coincides with the central portion 110 of the first embodiment described above, and the outer region formed by the second thermoplastic resin PC is the above-mentioned. Although the example which corresponds with the both ends 120 of 1st Embodiment was shown, an inner side area | region and an outer side area | region may be inconsistent with the center part 110 and the both ends 120, respectively. For example, as shown in FIG. 13 to be described later, the inner region made of the first thermoplastic resin PA has a shape covering a part of the outer region made of the second thermoplastic resin PC, and the inner region and the outer region are It may be inconsistent with the center part 110 and the both end parts 120, respectively.
In addition, the center part 110 of the film 100 before extending | stretching is a part which becomes a stretched film by heat-stretching by the extending process mentioned later. Further, both end portions 120 of the unstretched film 100 are for reinforcing the central portion 110 when the unstretched film 100 is heated and stretched, and are cut as necessary after the unstretched film 100 is stretched by heating. Can be removed. When cutting the unstretched film 100, it is desirable to completely remove both ends 120 by cutting part of both ends of the central portion 110. In this case, a part of both ends of the central portion 110 is also removed, but it is preferable to remove all portions held by the clip 310 described later.

In the pre-stretching film forming step, first, the first thermoplastic resin PA and the second thermoplastic resin PC are supplied to the T dice 220 through the feed block 210 in a state of being heated and melted.

In the present embodiment, the feed block 210 includes a first melt extruder (not shown) for melt-extruding the first thermoplastic resin PA and a melt-extrusion for the second thermoplastic resin PC. Second melt extruders (not shown) are connected to each other. These melt extruders are not particularly limited, and any of a single screw extruder and a twin screw extruder can be used. In the present embodiment, the first thermoplastic resin PA and the second thermoplastic resin PC are melt-extruded at a temperature equal to or higher than the melting point (melting) temperature by the respective melt extruders, thereby providing a feed block. 210 is supplied.

When the first thermoplastic resin PA and the second thermoplastic resin PC are supplied from the feed block 210 to the T dice 220, the unstretched film 100 obtained by the T dice 220 is as shown in FIG. In addition, the first thermoplastic resin PA and the second thermoplastic resin PA and the second thermoplastic resin PA are formed such that both end portions 120 made of the second thermoplastic resin PC are formed at both ends of the central portion 110 made of the first thermoplastic resin PA. The thermoplastic resin PC is supplied.

Specifically, the feed block 210 has an inlet for supplying the first thermoplastic resin PA and an inlet for supplying the first thermoplastic resin PA in the widening direction of the T die 220. On both sides, an inlet for supplying the second thermoplastic resin PC is separately provided. In the present embodiment, the first thermoplastic resin PA and the second thermoplastic resin PC respectively introduced from the inlet of the feed block 210 are merged in the feed block 210, and at the outlet of the feed block 210, T With respect to the widening direction of the die 220, the first thermoplastic resin PA flows in the central portion, and the second thermoplastic resin PC flows out in a manner such that the second thermoplastic resin PC flows in both end portions of the first thermoplastic resin PA. This is supplied to the T dice 220.

In the T die 220, the first thermoplastic resin PA and the second thermoplastic resin PC supplied from the feed block 210 are fed in the width direction (first thermal resin) by the manifold 221 provided in the T die 220. In the direction in which the plastic resin PA and the second thermoplastic resin PC are lined up), and thereby co-extruded from the die slip 222 into a sheet shape.

Next, the co-extruded sheet-like first thermoplastic resin PA and second thermoplastic resin PC are continuously taken up by the touch roll 230 and the cooling roll 240 as shown in FIG. And by solidifying the pre-stretched film 100 provided with a central portion 110 made of the first thermoplastic resin PA and both end portions 120 formed at both ends of the central portion 110 and made of the second thermoplastic resin PC. Make it.

And in this embodiment, the produced film 100 before extending | stretching is wound up by the film winding roll (not shown) before extending | stretching, and, thereby, the film 100 before extending | stretching can be obtained continuously. .

In addition, also in the film 100 before extending | stretching which consists of 1st thermoplastic resin PA and 2nd thermoplastic resin PC which are obtained in this way, the film 100 before extending | stretching which consists of a single thermoplastic resin in 1st Embodiment mentioned above. In the same manner as described above, a phenomenon called neck-in that shrinks in the width direction occurs after being melt-extruded from the die slip 222 of the T die 220 and taken up by the cooling roll 240.

Here, FIG. 8 is a diagram showing a cross section of the die slip 222 of the T-die 220 and the pre-stretching film 100 formed in the present embodiment, and the dimensions in the width direction of the die slip 222 and the pre-stretching formed. The relationship with the width of the film 100 is shown. In the present embodiment, when the pre-stretch film 100 is formed, the first thermoplastic resin PA and the second thermoplastic resin PC are melt-extruded by the T die 220 with the width of the die slip 222. Neck-in that shrinks in the width direction occurs as indicated by the arrow shown in FIG. 8 after being melt extruded and taken up by the cooling roll 240, and the width of the film 100 before stretching is the width of the die slip 222. Smaller than the direction dimension.

Such a neck-in is a portion where the thermoplastic resin melt-extruded from the T-die 220 contracts in the direction of the arrow shown in FIG. The inner region in the width direction of the front film 100 is shrunk in the thickness direction as indicated by the arrows, and the portions (that is, the outer regions in the width direction of the pre-stretching film 100) that are both ends 120 of the pre-stretching film 100 are indicated by the arrows As shown, it is generated by shrinking in the thickness direction and width direction. Then, the first thermoplastic resin PA and the second thermoplastic resin PC melt-extruded from the T die 220 are contracted by neck-in, so that the cross-sectional shape becomes as shown in FIG.

Here, FIG. 9 is a diagram for explaining the shrinkage of the melt-extruded first thermoplastic resin PA and second thermoplastic resin PC. In the present embodiment, the first thermoplastic resin PA and the second thermoplastic resin PC melt-extruded from the T-die 220 are portions that become the central portion 110 of the pre-stretch film 100 (see FIG. 9). In the inner region in the width direction), the flow direction of the thermoplastic resin is limited by the presence of the adjacent thermoplastic resin, so that the thermoplastic resin is aligned along the plane α located at or near the center of the thickness direction. Due to the planar expansion, the film contracts in the thickness direction as indicated by the arrow. On the other hand, the thermoplastic resin melt-extruded from the T-die 220 is formed on the outer side surfaces of both end portions 120 as shown in FIG. Since the adjacent thermoplastic resin does not exist, the thermoplastic resin flows relatively freely, and as a result, the uniaxial extension extending about the axis β passing through the center of the both ends 120 or near the center position is indicated by an arrow. As well as shrinking in the width direction in addition to the thickness direction. Thereby, between the center part 110 and the both ends 120, that is, between the inner region and the outer region in the width direction, a boundary portion 130 having a shape recessed in the thickness direction is formed due to the difference in the shrinking form of the thermoplastic resin. It is formed.

Therefore, in the pre-stretch film 100 formed by the method shown in FIG. 7, the boundary portion 130 between the central portion 110 and both end portions 120 is particularly thin as shown in FIG. In addition, FIG. 10 is a figure which shows an example of the result of having measured the thickness with respect to the position of the width direction about the film 100 before extending | stretching.

Here, when the thickness of the boundary portion 130 of the formed pre-stretching film 100 is too thin with respect to the thickness of the central portion 110, the boundary where the thickness is thin when the pre-stretching film 100 is heat stretched in the stretching step. There is a problem that cracks are likely to occur in the portion 130 and heating and stretching cannot be performed appropriately.

On the other hand, in this embodiment, as shown in FIG. 10, the average thickness of the central portion 110 is t _c for the unstretched film 100 formed by being melt-extruded by the T-die 220 and taken by the cooling roll 240. When the minimum thickness of the boundary 130 is t _b , the ratio of these thicknesses “t _b / t _c ” is adjusted to 0.75 or more to heat the unstretched film 100 as will be described later. When stretching, the boundary 130 can be effectively prevented from cracking, and the productivity of the stretched film can be improved.

Note that the average thickness t _c of the central portion 110 shown in FIG. 10 is the average value of the thickness of the portion where the thickness of the central portion 110 is stable. For example, the thickness is ± 5 based on the center of the central portion 110. It can be an average value of thickness in a region within ˜10%. As the minimum thickness t _b of the boundary portion 130, of the two minimum thickness of the boundary portion 130 of the pre-stretch film 100, a more thinner thickness.

<Extension process>
The stretching step is a step of heating and stretching the pre-stretching film 100 obtained by the pre-stretching film forming step in the length direction and the width direction. Here, FIG. 11 is a figure for demonstrating an extending process. In the present embodiment, in the stretching step, the unstretched film winding roll 100 is fed out from the unstretched film take-up roll described above, and the length of the stretched film 100 is gripped by the clips 310 as shown in FIG. The film 100 before stretching is heated and stretched by a simultaneous biaxial stretching method in which the film and the width direction are simultaneously stretched.

Specifically, in the stretching step, the unstretched film 100 is continuously fed out from the unstretched film winding roll, and the two ends 120 of the unstretched film 100 are gripped at regular intervals using a plurality of clips. The unstretched film 100 is conveyed into the stretching furnace 320 by 310, and in the stretching furnace 320, the unstretched film 100 is pulled in the length direction and the width direction by the respective clips 310. At this time, the unstretched film 100 is transported while being held by the clip 310, so that it passes through the stretching furnace 320, and is stretched in the pre-tropical zone in the stretching furnace 320. The pre-film 100 is preheated to a temperature about 10 to 30 ° C. higher than the glass transition temperature of the second thermoplastic resin PC at both ends 120 constituting the front film 100, and then in the stretching zone in the stretching furnace 320, It is pulled in the length direction and the width direction by the clip 310 while keeping heat, and is stretched in the length direction and the width direction. And a stretched film can be obtained by cooling and solidifying in the cooling heat fixed zone following this. And the stretched film can be obtained continuously by opening the clip 310 and winding up with a roll.

In the present embodiment, a pair of guide rails for moving the clip 310 so as to pass through the drawing furnace 320 is provided. The pair of guide rails are respectively installed at the position of the clip 310 that holds the upper ends 120 of the pre-stretch film 100 shown in FIG. 11 and the position of the clip 310 that holds the lower ends 120. In the pre-tropical zone in the furnace 320, they are parallel to each other, in the stretching zone, they are separated from each other in the width direction of the pre-stretching film 100, and in the cooling heat fixing zone, they are also parallel to each other. Alternatively, in the cooling heat fixing band, the distance between the pair of guide rails in the cooling heat fixing band is determined in consideration of the shrinkage when the stretched film heated and stretched in the stretching band is solidified. On the basis of the width of the stretched film on the side, it may be approximated by several percent in the width direction. In the present embodiment, the clip 310 that holds the both end portions 120 of the unstretched film 100 moves along such guide rails so that the unstretched film 100 can be conveyed and stretched.

In this embodiment, the pre-stretching film 100 is stretched in the stretching zone in the stretching furnace 320 using the clip 310 that moves along such a guide rail. That is, in the stretching zone in the stretching furnace 320, the clip 310 holding the both ends 120 of the unstretched film 100 is moved so as to spread in the width direction along the guide rail, and the interval between the clips 310 is also increased. By performing the spreading control, both end portions 120 of the unstretched film 100 are pulled in the length direction and the width direction as indicated by arrows in FIG. Thereby, the center part 110 and the both ends 120 of the film 100 before extending | stretching are heat-stretched until it becomes a draw ratio required in a length direction and the width direction, respectively. And the film 100 before extending | stretching heat-stretched is cooled and solidified in the cooling heat fixed zone in the extending furnace 320, and is wound up with the roll installed outside the extending furnace 320, and, thereby, continuous Thus, a stretched film can be obtained.

In this embodiment, it is possible to obtain a stretched film by making the stretching step and the pre-stretching film forming step into a continuous line (step).

In the present embodiment, the thickness of the central portion 110 of the unstretched film 100 after heat stretching is preferably 15 to 50 μm, more preferably 20 to 40 μm. By controlling the thickness of the central portion 110 of the pre-stretching film 100 after heat stretching within the above range, it is possible to prevent the pre-stretching film 100 from being broken during the heat stretching and appropriately heat-stretch the pre-stretching film 100. it can.

In the present embodiment, the stretched film obtained by heating and stretching the pre-stretched film 100 may be removed by cutting both ends 120 as necessary. Thereby, a stretched film can be made into the film which consists only of the center part 110. FIG.

As described above, in the present embodiment, before stretching, the pre-stretching film forming step includes the central portion 110 made of the first thermoplastic resin PA and the both end portions 120 made of the second thermoplastic resin PC. A stretched film can be obtained by forming the film 100 and heating and stretching the central portion 110 and both end portions 120 of the unstretched film 100 by a stretching step.

Here, in the present embodiment, when the pre-stretch film 100 is formed by the pre-stretch film forming step, the ratio “t _b ” between the average thickness t _c of the central portion 110 and the minimum thickness t _b of the boundary portion 130. The thickness of the unstretched film 100 is adjusted so that “/ t _c ” is 0.75 or more. Thereby, when heat-stretching the film 100 before extending | stretching at an extending | stretching process, generation | occurrence | production of the crack in the boundary part 130 with thin thickness can be prevented effectively, and productivity of a stretched film can be improved.

In addition, when the film 100 before extending | stretching is heat-stretched, the boundary part 130 among the films 100 before extending | stretching has a low extending | stretching stress required for extending | stretching by thinness, and will be extended preferentially. As the stretching proceeds at the boundary portion 130, the stretching stress at the boundary portion 130 gradually increases, and when the stretching stress necessary for stretching at the central portion 110 is reached, the central portion 110 is also stretched following the boundary portion 130. Become so. At this time, if the thickness of the boundary portion 130 is too thin with respect to the central portion 110, the boundary portion 130 breaks before the central portion 110 starts to be stretched while the boundary portion 130 is being stretched. End up. Further, if the thickness of the boundary portion 130 is too thin with respect to the central portion 110, after the heat stretching as shown in FIG. 11, the impact when releasing the unstretched film 100 from the clip 310, and the obtained stretched film Cracks are also generated in the boundary portion 130 due to the stress at the time of winding on the roll.

Here, conventionally, as a method for preventing breakage of the film during heat stretching by simultaneous biaxial stretching, a method of forming both end portions of the film before heat stretching thicker than the central portion is known. However, when the film to be stretched is produced by melt extrusion using the T-die 220, the boundary formed between the center portion and both end portions of the film even if both end portions of the film are thickened as described above. As shown in FIG. 9, the thickness of the portion is reduced, and there is a problem that a crack occurs at such a boundary portion when the film is heated and stretched. In FIG. 9 described above, an example in which different thermoplastic resins are used in the central portion 110 and the both end portions 120 is shown. However, when the central portion 110 and the both end portions 120 are formed of the same thermoplastic resin (that is, In the same way, when the film 100 before stretching shown in FIG. 9 is a single-layer film made of one kind of resin, when being melt-extruded from the T-die 220, the central portion 110 (inner region in the width direction) ) And the end portion 120 (outer region in the width direction), the boundary portion becomes thin due to the difference in the contraction form of the thermoplastic resin.

On the other hand, according to this embodiment, after the film co-extrusion by the T-die 220 and the film 100 before stretching formed by being drawn by the cooling roll 240, the average thickness t _c of the central portion 110 and the boundary portion 130 By adjusting the ratio “t _b / t _c ” to the minimum thickness t _b within the above range, it is possible to effectively prevent the occurrence of cracks at the boundary 130 when the film 100 before stretching is heated and stretched, Productivity of the stretched film can be improved.

Further, conventionally, in order to prevent breakage of the unstretched film 100 during heat stretching, rubber elastic particles are added to both end portions 120 of the unstretched film 100 to soften the both end portions 120 (breaking elongation at normal temperature). The method of increasing the rate is known. However, this method has the following problems because the rubber elastic particles in both end portions 120 are easily deteriorated by heat. That is, when the film 100 before stretching is melt-coextruded from the T die 220, rubber elastic particles deteriorated by heat are deposited on the die slip 222 of the T die 220 to form a deposit. Therefore, there is a possibility that the film 100 before being stretched may be imprinted, or that a deposit may be mixed in the product roll of the stretched film and deteriorate the quality of the stretched film. Further, when such a deposit of rubber elastic particles is formed, when the film 100 before stretching is heated and stretched using the clip 310 as shown in FIG. There is also a risk that the deposit will enter the film, and the pre-stretched film 100 may be easily broken.

On the other hand, according to this embodiment, it is not necessary to add such rubber elastic particles to both end portions 120 of the unstretched film 100, or the amount of rubber elastic particles added to both end portions 120 is small. Therefore, precipitation of rubber elastic particles during melt coextrusion of the unstretched film 100 can be suppressed, and the resulting stretched film can be excellent in quality.

In the present embodiment, the ratio “t _b / t _c ” between the average thickness t _c of the central portion 110 and the minimum thickness t _b of the boundary portion 130 may be 0.75 or more as described above. , Preferably 0.8 or more, more preferably 0.9 or more.

In the present embodiment, the ratio “t _b / t _c ” between the average thickness t _c of the central portion 110 and the minimum thickness t _b of the boundary portion 130 is adjusted to the above range for the pre-stretch film 100 to be formed. There are no particular restrictions on the method used, for example, a method using a resin having a lower extensional viscosity as the thermoplastic resin, a method of adjusting the slit width of the die slip 222 of the T die 220, and the method of using the T die 220 and the cooling roll 240. A method of reducing the distance, a method of reducing the take-up speed of the pre-stretching film 100 by the cooling roll 240, or the like can be used alone or in combination.

In this embodiment, among these methods, the type of applicable thermoplastic resin is not limited, and the slit width of the die slip 222 is adjusted from the viewpoint of not reducing the production efficiency of the pre-stretching film 100. It is preferable to use the method to do. At this time, when the slit width of the die lip 222 was _{t s,} the ratio _"t s / _{t c"} of the average thickness _{t c} of the slit width _{t s} and the central portion 110 of the die lip 222, preferably It adjusts so that it may be 8.0 or less, More preferably, it is 6.0 or less, More preferably, it is 5.0 or less. Thereby, the thickness of the unstretched film 100 obtained by melt extrusion with the T die 220 can be made more uniform, and the ratio “t _b ” between the average thickness t _c of the central portion 110 and the minimum thickness t _b of the boundary portion 130. / T _c ”can be appropriately adjusted to the above range.

In the present embodiment, the pre-stretched film 100 to be formed, the ratio _"t b / _{t c"} with minimum thickness _{t b} of the average thickness _{t c} and the boundary portion 130 of the central portion 110 as described above the In addition to adjusting to the range, by adjusting the maximum thickness of the both end portions 120 so as to be moderate, it is possible to more effectively prevent the pre-stretching film 100 from being broken during the heat stretching.

Specifically, in the case of forming the pre-stretch film 100, as shown in FIG. 10, the maximum thickness of the end portions 120 when the t _e, the average of the maximum thickness t _e and the central portion 110 of the end portions 120 The ratio “t _e / t _c ” with _respect to the thickness t _c is preferably adjusted to 1.0 to 3.0, more preferably 1.0 to 2.0, and still more preferably 1.0 to 1.5. Here, the maximum thickness t _e of the ends 120, of the thickness of the end portions 120 of the pre-stretched film 100 (the one end portion and another end portion in the width direction), and more thicker thickness. Incidentally, in the case with respect to the average thickness _{t c} of the central portion 110, the maximum thickness _{t e} of the end portions 120 is too thick, the unstretched film 100 obtained by melt co-extrusion by a T die 220, the touch roll 230 and the cooling When pinching with the roll 240, the both end portions 120 are too thick, so that the pressure is concentrated on the both end portions 120 and the pressure is not uniformly transmitted to the whole unstretched film 100, and thereby the thickness of the unstretched film 100 varies. The thickness of the stretched film obtained by heating and stretching the pre-stretching film 100 also tends to vary. On the other hand, with respect to the average thickness t _c of the central portion 110, when the maximum thickness t _e of the end portions 120 is too thin, the time of pre-stretched film 100 is melt coextruded by a T-die 220 is neck-both ends There is a tendency that the portion 120 pulls the thermoplastic resin at the boundary portion 130, thereby making the boundary portion 130 thinner, and the pre-stretching film 100 is liable to break during heating and stretching.

In the present embodiment, the first thermoplastic resin PA for forming the central portion 110 may be selected according to the intended use of a stretched film, such as an acrylic resin (PMMA). , Cyclic olefin copolymer (COC) and the like can be used.

As the second thermoplastic resin PC for forming the end portions 120, for example, the glass transition temperature Tg ₁ of the first thermoplastic resin PA, glass transition temperature Tg ₂ of the second thermoplastic resin PC It is preferable to use a thermoplastic resin having a difference (| Tg ₁ −Tg ₂ |) of 10 ° C. or less. Thereby, in this embodiment, when the both ends 120 of the film 100 before extending | stretching are hold | gripped by the clip 310 and heat extending | stretching by the extending | stretching process, the both ends 120 hold | gripped by the clip 310 are heated by the drawing furnace 320. Softening moderately prevents the clip from being removed during heating and stretching, breakage of the film 100 before stretching, and the like, and the productivity of the stretched film can be improved.

In this case, the difference in glass transition temperature between the first thermoplastic resin PA and the second thermoplastic resin PC (| Tg ₁ −Tg ₂ |) is preferably 10 ° C. or less, more preferably 5 ° C. Hereinafter, it is 3 degrees C or less more preferably.

In the present embodiment, as the second thermoplastic resin PC, specifically, the following thermoplastic resin can be used based on the viewpoint described above. For example, as the second thermoplastic resin PC, when an acrylic resin is used for the first thermoplastic resin PA, one kind of polyethylene naphthalate (PEN), cyclic olefin polymer (COP), etc. is used alone. Use or a mixed resin in which two or more kinds are mixed can be used.

Further, as the second thermoplastic resin PC, a resin obtained by adding a small amount of rubber elastic particles to the above-described first thermoplastic resin PA within a range not inhibiting the productivity of the stretched film may be used.

Alternatively, the second thermoplastic resin PC has a glass transition temperature higher than that of the first thermoplastic resin PA, and the difference between the thermoplastic resin (heat-resistant thermoplastic resin) exceeding 10 ° C. A mixed resin formed by blending a thermoplastic resin (low temperature meltable thermoplastic resin) having a glass transition temperature lower than that of the first thermoplastic resin PA can be used. In this case, the glass transition temperature of the obtained mixed resin is adjusted with the first thermoplastic resin PA by adjusting the blending ratio of the heat-resistant thermoplastic resin and the low-melting thermoplastic resin. The glass transition temperature difference (| Tg ₁ −Tg ₂ |) is preferably adjusted to be in the above range.

For example, when an acrylic resin having a glass transition temperature Tg ₁ of about 120 ° C. is used as the first thermoplastic resin PA, a polycarbonate having a high glass transition temperature of about 150 ° C. is used as the second thermoplastic resin PC. (PC) blended with polyethylene terephthalate (PET) having a low glass transition temperature of about 70 ° C., and using a mixed resin in which the glass transition temperature is adjusted to around 120 ° C., which is about the same as the glass transition temperature Tg _1. it can.

When such a mixed resin is used as the second thermoplastic resin PC, polycarbonate (PC), cyclic olefin polymer (COP), or the like can be used as the heat-resistant thermoplastic resin. Further, as the low-melting thermoplastic resin, polyester such as polyethylene terephthalate (PET) and polyethylene naphthalate (PEN), acrylonitrile / butadiene / styrene (ABS), polyethylene (PE), glass from the first thermoplastic resin. An acrylic resin, polyester (PEs), polybutylene terephthalate (PBT), or the like having a low transition temperature can be used. In the present embodiment, among these, polycarbonate (PC) is used as a heat-resistant thermoplastic resin, and polyethylene terephthalate (polyethylene terephthalate (low-melting thermoplastic resin) is used from the viewpoint that it is easy to adjust the glass transition temperature of the resulting mixed resin. It is preferable to use (PET).

Here, FIG. 12 is a graph showing the results of measuring the glass transition temperature of a mixed resin obtained by blending polyethylene terephthalate (PET) with polycarbonate (PC). In FIG. 12, the glass transition temperature of the resin having a polyethylene terephthalate (PET) content of 0%, 25%, 50%, 75%, 100% with respect to polycarbonate (PC) is measured by differential scanning calorimetry ( DSC) shows the measurement results. Here, in the measurement by differential scanning calorimetry (DSC), regardless of the content ratio of polyethylene terephthalate (PET), the glass transition temperature of the mixed resin is determined to be almost one point without becoming broad. Yes.

As shown in FIG. 12, the mixed resin in which polycarbonate (PC) is blended with polyethylene terephthalate (PET) can change the glass transition temperature according to the content ratio of polyethylene terephthalate (PET). Thereby, in this embodiment, when such a mixed resin is used as the second thermoplastic resin, the glass transition temperature Tg ₂ of the _second thermoplastic resin PC can be easily adjusted. The difference (| Tg ₁ −Tg ₂ |) between the glass transition temperature Tg ₁ and the other thermoplastic resin PA can be controlled within the above range.

In the present embodiment, it is preferable to smooth the side surfaces of both end portions 120 before heating and stretching the pre-stretch film 100 formed by the pre-stretch film forming step. By smoothing the side surfaces of both end portions 120 of the pre-stretching film 100, when the pre-stretching film 100 is heated and stretched by pulling the both end portions 120 of the pre-stretching film 100 in the stretching step, Concentration of local stress due to roughness can be prevented, generation of tears at both ends 120 can be prevented, and productivity of the stretched film can be improved.

The method for smoothing the side surfaces of both end portions 120 of the unstretched film 100 is not particularly limited, but a method of trimming a predetermined width from both side surfaces of both end portions 120 with a cutter, a method for polishing the end portions of both end portions 120, For example, a method of heat-pressing the end portions of the both end portions 120 can be used. The smoothing of the side surfaces of both end portions 120 reduces the unevenness of the side surfaces of both end portions 120, and when the pre-stretch film 100 is pulled in the length direction, stress is not concentrated on a part of both end portions 120. Just go to

When trimming the both ends 120 of the unstretched film 100 with a cutter, any cutter can be used as long as it can smoothly smooth the side surfaces of both ends 120 by trimming. You can use a rotary shear cutter that continuously rotates while rubbing the blade and lower blade and cut by shearing, or a laser cutter that uses a solid laser, semiconductor laser, liquid laser, gas laser, etc. A laser cutter is preferable from the viewpoint that the stress applied to the unstretched film 100 can be reduced and the occurrence of cracks in the unstretched film 100 during trimming can be prevented.

In addition, when trimming both end portions 120 of the pre-stretched film 100, it is preferable to trim the both end portions 120 while heating. Thereby, the side surfaces of both end portions 120 can be made smoother, and breakage of the pre-stretching film 100 when the pre-stretching film 100 is heated and stretched can be more appropriately prevented.

Moreover, in the example mentioned above, as shown in FIG. 11, as a method of heating and stretching the film 100 before stretching, a simultaneous biaxial stretching method in which the film 100 before stretching is heated and stretched in both the length direction and the width direction is used. Although the example used is shown, in this embodiment, you may use the method of uniaxially stretching the film 100 before extending | stretching only to a length direction.

In this case, the heat stretching in the length direction of the pre-stretching film 100 can be performed in the same manner as the simultaneous biaxial stretching method shown in FIG. In other words, the clips 310 are conveyed into the stretching furnace 320 while holding the both ends 120 of the unstretched film 100 with the clips 310, and then each clip 310 holding the both ends 120 of the unstretched film 100 in the stretching furnace 320. A method of performing heat stretching only in the length direction can be used by widening the interval between the clips 310 without moving the clip in the width direction.

In the present embodiment, both end portions of the unstretched film 100 as shown in FIG. 11 in both the case where simultaneous biaxial stretching is performed in the length direction and the width direction, and the case where uniaxial stretching is performed only in the length direction. By stretching 120 while holding it with the clip 310, the productivity of the stretched film can be improved as compared with the conventionally used sequential biaxial stretching method, and the resulting stretched film can be improved in quality. It can be excellent.

The conventional sequential biaxial stretching method is a method in which the pre-stretched film 100 produced by the method shown in FIG. 7 is first stretched by heating in the length direction and then stretched in the width direction. In the sequential biaxial stretching method, the film 100 before stretching is heated and stretched in the length direction by being conveyed by a plurality of rolls, and thereafter, both ends 120 of the film 100 before stretching are clipped by clips 310 as shown in FIG. Heat and stretch in the width direction while gripping.

Here, the stretching in the length direction of the pre-stretching film 100 in the sequential biaxial stretching method is specifically performed as follows. That is, according to the sequential biaxial stretching method, the pre-stretched film 100 is preheated to about the glass transition temperature of both end portions 120 while being transported by a plurality of preheated rolls that have been preheated. While being further heated to a temperature about 10 to 30 ° C. higher than the glass transition temperature of the both ends 120 by an infrared heater or the like, it is continuously conveyed by a cooling roll. At this time, by making the conveyance speed by the cooling roll faster than the conveyance speed by the pre-tropical roll, a tension is generated between the pre-tropical roll and the cooling roll. Is stretched in the length direction to a necessary stretching ratio.

Here, in the sequential biaxial stretching method, when the pre-stretching film 100 is stretched in the length direction, the surface of the pre-stretching film 100 comes into contact with the preheating roll and the cooling roll. Scratches may occur on the surface, and the appearance quality of the obtained stretched film may be deteriorated. Further, in the sequential biaxial stretching method, when the film 100 before stretching is heated and stretched in the length direction, since the both ends 120 of the film 100 before stretching are not fixed with clips or the like, the film 100 before stretching is heated. There exists a possibility that it may shrink | contract in the width direction and productivity of a stretched film may fall.

On the other hand, according to this embodiment, the film 100 before stretching is stretched in the length direction by using the simultaneous biaxial stretching method described above or the method of uniaxial stretching only in the length direction described above. (That is, by using a method of stretching in the length direction while holding both ends 120 of the unstretched film 100 with the clip 310 as shown in FIG. 11) to avoid contact with the roll. Therefore, scratches on the surface of the pre-stretching film 100 after heat stretching can be reduced. Thereby, about the stretched film obtained by cutting the both ends 120 of the pre-stretched film 100 that has been heat-stretched, the appearance quality can be improved, and in particular, it is preferably used for an optical film or the like that has a severe requirement for the appearance quality. Can do. Furthermore, according to the present embodiment, when the film 100 before stretching is stretched in the length direction, the both ends 120 of the film 100 before stretching are gripped by the clips 310. Shrinkage in the direction can be prevented, and the productivity of the stretched film can be improved.

Moreover, in the example mentioned above, as shown in FIG. 9, the unstretched film 100 includes a central portion 110 made of the first thermoplastic resin PA and both end portions 120 made of the second thermoplastic resin PC. In the embodiment, the first thermoplastic resin PA and the second thermoplastic resin PC are within a range that does not hinder the production of the stretched film. It may be mixed.

For example, as the unstretched film 100, the viscosity of the second thermoplastic resin PC that forms the outer region of the unstretched film 100 is equal to the viscosity of the first thermoplastic resin PA that forms the inner region of the unstretched film 100. In contrast, as shown in FIG. 13, the center portion 110 may have a shape that covers a part of both end portions 120 as shown in FIG. 13. In this case, the boundary portion 130 of the unstretched film 100 is formed at a position shifted from the boundary between the central portion 110 and both end portions 120.

That is, as described above, the boundary portion 130 of the unstretched film 100 is recessed in the thickness direction due to the difference in shrinkage between the inner region and the outer region in the width direction of the thermoplastic resin melt-extruded from the T die 220. It is formed by the end. Therefore, as shown in FIG. 13, the pre-stretch film 100 in which the first thermoplastic resin and the second thermoplastic resin are mixed is formed by the difference in contraction form depending on the position in the width direction of the pre-stretch film 100. The boundary portion 130 to be formed is formed at a position deviated from the boundary between the first thermoplastic resin PA and the second thermoplastic resin PC.

In addition, when performing melt coextrusion with the T-die 220, when the viscosity of the second thermoplastic resin PC is higher than the viscosity of the first thermoplastic resin PA, in the obtained pre-stretch film 100, Contrary to the unstretched film 100 shown in FIG. 13, the second thermoplastic resin PC having a higher viscosity flows on the surface of the central portion 110 and covers a part of the first thermoplastic resin PA. Become.

Hereinafter, the present invention will be described more specifically with reference to examples, but the present invention is not limited to these examples.

<Example 1>
An acrylic resin (glass transition temperature Tg ₁ : 123 ° C., elongation at break at room temperature: 5%) was prepared as a thermoplastic resin for forming the pre-stretch film 100.

Here, for the prepared thermoplastic resin, the glass transition temperature was measured by differential scanning calorimetry (DSC), and the elongation at break was measured by a tensile tester (manufactured by Orientec Co., Ltd., model number: RTC-1210A). The same applies to Example 2 and Comparative Example 1 below.

Next, using the prepared thermoplastic resin, as shown in FIG. 1, a pre-stretch film 100 was produced under the following conditions. Here, the produced unstretched film 100 had an overall width of about 310 mm. Then, when the pre-stretched film 100 manufactured was measured thickness, the average thickness _{t c} of the central portion 110 is 160 .mu.m, the minimum thickness _{t b} of the boundary portion 130 is 128 .mu.m, the maximum thickness _{t e} of the both end portions 120 in 290μm The thickness ratio “t _b / t _c ” was 0.8, “t _e / t _c ” was 1.81, and “t _s / t _c ” was 5.0. The results are shown in FIG. Here, in FIG. 6A and FIGS. 6B and 6C described later, the thickness corresponding to the position in the width direction of the unstretched film 100 is shown. In addition, as shown to FIG. 6 (A), the boundary part 130 of the film 100 before extending | stretching was formed in the position of each about 40 mm from the edge part of the width direction of the film 100 before extending | stretching.
T-die 220 outlet width direction dimension: 380mm
Slit width t _s of die slip 222: 0.8 mm
Distance between T dice 220 and cooling roll 240: 60 mm
Take-up speed of cooling roll 240: 5 mpm

Next, the obtained unstretched film 100 is gripped by a clip 310 and, as shown in FIG. 5, is stretched by heating in the length direction and the width direction under the following conditions by a simultaneous biaxial stretching method, and then by a roll. A stretched film was obtained by winding. In this example, the film 100 before stretching did not break while the film 100 before stretching was heated and stretched. Further, when the thickness of the stretched film obtained was measured, the thickness of the portion corresponding to the boundary portion 130 was comparatively thick at 30 μm or more, and the product effective width (region having a thickness of 40 μm or more at the central portion 110) was 390 mm. A stretched film secured relatively widely could be obtained. The results are shown in FIG.
Stretcher entrance speed: 1 mpm
Outlet speed of stretching machine: 2 mpm
Stretch ratio: 100% in length direction x 100% in width direction (twice in length direction x double in width direction)
Clip 310 gripping position: position 15 mm from the end of the film 100 before stretching Pretropical temperature, distance: 140 ° C., 350 mm
Stretch zone temperature, distance: 140 ° C., 500 mm
Cooling heat fixing temperature, distance: 90 ° C, 700mm

<Example 2>
In making the pre-stretch film 100, except that was enlarged slit width t _s of die lip 222 to 1.2mm, with the pre-stretch film 100 and a stretched film in the same manner as in Example 1, measuring the thickness did. The result of having measured thickness about the film 100 before extending | stretching and a stretched film is shown to FIG. 6 (B).

In Example 2, the produced unstretched film 100 has an average thickness t _c of the central portion 110 of 160 μm and a minimum thickness t _b of the boundary portion 130 of 120 μm, and the ratio of these thicknesses “t _b / t _c ”. but 0.75, _"t s / _{t c"} was 7.5. Moreover, in Example 2, compared with Example 1 mentioned above, the boundary part 130 of the film 100 before extending | stretching before heat drawing becomes thin, and, as a result, the stretched film after heat drawing is shown in FIG. As shown, the product effective width (region having a thickness of 40 μm or more in the central portion 110) was reduced.

However, also in Example 2, as in Example 1, while the film 100 before stretching was heated and stretched, the film 100 before stretching did not break, and a stretched film excellent in quality was continuously produced. We were able to.

<Comparative Example 1>
While increasing the extrusion amount of the thermoplastic resin by the T dice 220 and increasing the take-up speed of the cooling roll 240 to 15 mpm, the film 100 before stretching and the stretched film were obtained in the same manner as in Example 1, and the thickness was increased. It was measured. The result of having measured thickness about the film 100 before extending | stretching and a stretched film is shown in FIG.6 (C).

In Comparative Example 1, the produced unstretched film 100 has an average thickness t _c of the central portion 110 of 158 μm and a minimum thickness t _b of the boundary portion 110 of 110 μm, and the ratio of these thicknesses “t _b / t _c ”. Was 0.70.

In Comparative Example 1, in the prepared film 100 before stretching, the minimum thickness t _b of the boundary portion 130 was too thin with respect to the average thickness t _c of the central portion 110. Cracks occurred in the boundary portion 130 of the front film 100, the breakage of the pre-stretch film 100 occurred frequently, and the productivity of the stretched film was reduced. Here, in Comparative Example 1, the frequency of pre-stretching film 100 at the time of heat stretching is reduced by changing the temperature of the pre-tropical zone and the stretch zone during heat stretching from 140 ° C. to 150 ° C. Although the obtained stretched film had a very small minimum thickness of about 8 μm in the portion corresponding to the boundary portion 130, the stress at the time of releasing the clip 310 from the stretched film after heat stretching. In addition, due to the stress when winding the obtained stretched film on a roll, a crack was generated in a portion corresponding to the boundary portion 130, and the stretched film was broken.

As described above, the ratio “t _b / t _c ” of the minimum thickness t _b of the boundary portion 130 to the average thickness t _c of the central portion 110 is 0.75 or more for the pre-stretch film 100 before performing the heat stretching. In Examples 1 and 2, when the pre-stretched film 100 was heated and stretched, it was possible to suppress breakage of the pre-stretched film 100, so that it was possible to obtain a stretched film excellent in quality, and production of a stretched film It was possible to improve the performance. In particular, Examples 1 and 2, with respect to the average thickness _{t c} of the central portion 110, since the ratio of the slit width _{t s} of die lip 222 _"t s / _{t c"} was 8.0 or less, in FIG. 6 (A) As shown, the obtained stretched film had a uniform thickness and excellent quality.

On the other hand, as described above, the ratio “t _b / t _c ” of the minimum thickness t _b of the boundary portion 130 to the average thickness t _c of the central portion 110 is 0.75 for the unstretched film 100 before heat stretching. In Comparative Example 1, which was less than the above, during the heat stretching of the pre-stretched film 100, the pre-stretched film 100 was frequently broken, resulting in poor stretched film productivity.

<Example 3>
An acrylic resin (glass transition temperature Tg ₁ : 123 ° C., elongation at break at room temperature: 5%) is prepared as the first thermoplastic resin PA for forming the central portion 110 of the film 100 before stretching, and the film before stretching As a second thermoplastic resin PC for forming both end portions 120 of 100, an acrylic resin (glass transition temperature Tg ₂ : 125 ° C., elongation at break at room temperature: 7%) added with a small amount of rubber elastic particles is prepared. did.

Here, for the first thermoplastic resin PA and the second thermoplastic resin PC, the glass transition temperature is measured by differential scanning calorimetry (DSC), and the elongation at break at room temperature is measured by a tensile tester (Orientec Co., Ltd.). Manufactured, model number: RTC-1210A). The same applies to Example 4 and Comparative Example 2 below.

Next, the prepared first thermoplastic resin PA and second thermoplastic resin PC are respectively supplied to the feed block 210 by a twin-screw extruder, and by the method shown in FIG. Was made. Here, the produced unstretched film 100 had an overall width of about 315 mm. Then, when the pre-stretched film 100 manufactured was measured thickness, the average thickness _{t c} of the central portion 110 is 160 .mu.m, the minimum thickness _{t b} of the boundary portion 130 133Myuemu, maximum thickness _{t e} of the both end portions 120 in 270μm The thickness ratio “t _b / t _c ” was 0.83, “t _e / t _c ” was 1.69, and “t _s / t _c ” was 5.0. The results are shown in FIG. Here, in FIG. 14A, FIG. 14B and FIG. 14C described later, the thickness corresponding to the position in the width direction of the unstretched film 100 is shown. As shown in FIG. 14A, the boundary portion 130 of the unstretched film 100 was formed at a position of about 50 mm from the end portion in the width direction of the composite film 100. In this example, an acrylic resin to which rubber elastic particles were added was used as the second thermoplastic resin PC. However, since the amount of the rubber elastic particles added was small, the film 100 before stretching was melt-coextruded. It was possible to suppress the precipitation of rubber elastic particles during the process.
T-die 220 outlet width direction dimension: 380mm
Slit width t _s of die slip 222: 0.8 mm
Distance between T dice 220 and cooling roll 240: 60 mm
Take-up speed of cooling roll 240: 6 mpm
Supply amount of first thermoplastic resin PA to feed block 210: 15 kg / hr
Supply amount of second thermoplastic resin PC to feed block 210: 5 kg / hr

Next, the obtained unstretched film 100 is gripped at both ends 120 by clips 310 and heated and stretched in the length direction and the width direction under the following conditions by the simultaneous biaxial stretching method as shown in FIG. Then, a stretched film was continuously obtained by winding with a roll. In this example, the film 100 before stretching did not break while the film 100 before stretching was heated and stretched. Furthermore, when the thickness of the obtained stretched film was measured, the thickness of the portion corresponding to the boundary portion 130 was relatively thick as 30 μm or more, and the product effective width (region having a thickness of 40 μm or more in the central portion 110) was 450 mm. A stretched film secured relatively widely could be obtained. The results are shown in FIG.
Entry speed before heat drawing: 1 mpm
Outlet speed after heating and stretching: 2 mpm
Stretch ratio: 100% in length direction x 100% in width direction (twice in length direction x double in width direction)
Clip 310 gripping position: 15 mm from the end of the composite film 100 Pre-tropical temperature, distance: 140 ° C., 350 mm
Stretch zone temperature, distance: 140 ° C., 500 mm
Cooling heat fixing temperature, distance: 90 ° C, 700mm

<Example 4>
In making the pre-stretch film 100, except that was enlarged slit width t _s of die lip 222 to 1.2mm, with the pre-stretch film 100 and a stretched film in the same manner as in Example 3, measuring the thickness did. The result of having measured thickness about the film 100 before extending | stretching and a stretched film is shown to FIG. 14 (B).

In Example 4, the produced unstretched film 100 has an average thickness t _c of the central portion 110 of 147 μm and a minimum thickness t _b of the boundary portion 110 of 110 μm, and the ratio of these thicknesses “t _b / t _c ”. Was 0.75. Moreover, in Example 4, although compared with Example 3 mentioned above, as shown in FIG.14 (B), although the boundary part 130 of the film 100 before extending | stretching before heating extending | stretching was a little thin, Example 1 and Similarly, precipitation of rubber elastic particles during melt coextrusion of the pre-stretching film 100 can be suppressed, and further, the pre-stretching film 100 does not break while the pre-stretching film 100 is heated and stretched. A stretched film excellent in quality could be continuously produced.

<Comparative example 2>
As the second thermoplastic resin PC for forming both end portions 120 of the unstretched film 100, an acrylic resin (glass transition temperature Tg ₂ : 125 ° C., elongation at break at room temperature: increased amount of rubber elastic particles added: Except for using 28%), a film 100 before stretching and a stretched film were obtained in the same manner as in Example 3, and the thickness was measured. The result of having measured thickness about the film 100 before extending | stretching and a stretched film is shown in FIG.14 (C).

In Comparative Example 2, the produced unstretched film 100 has an average thickness t _c of the central portion 110 of 155 μm and a minimum thickness t _b of the boundary portion of 102 μm, and the ratio of these thicknesses “t _b / t _c ”. Was 0.66.

In Comparative Example 2, since the minimum thickness t _b of the boundary portion 130 was too thin with respect to the average thickness t _c of the central portion 110 in the produced pre-stretch film 100, the pre-stretch film 100 was heated and stretched. Cracks occurred in the boundary portion 130 of the pre-stretched film 100, and the pre-stretched film 100 was frequently broken, resulting in reduced stretched film productivity.

As described above, with respect to the unstretched film 100 before heat stretching, the ratio “t _b / t _c ” of the minimum thickness t _b of the boundary portion 130 to the average thickness t _c of the central portion 110 was set to 0.75 or more. In Examples 3 and 4, when the pre-stretched film 100 was heated and stretched, the pre-stretched film 100 could be prevented from being broken, so that a stretched film excellent in quality could be obtained. I was able to improve. In particular, Example 3, with respect to the average thickness _{t c} of the central portion 110, since the ratio _"t s / _{t c"} of the slit width _{t s} of die lip 222 and 8.0 or less, as shown in FIG. 14 (A) Furthermore, the obtained stretched film had a uniform thickness and an excellent quality.

On the other hand, as described above, the ratio “t _b / t _c ” of the minimum thickness t _b of the boundary portion 130 to the average thickness t _c of the central portion 110 is less than 0.75 for the unstretched film 100 before heat stretching. In Comparative Example 2, the film 100 before stretching was frequently broken during the heat stretching of the film 100 before stretching, and the productivity of the stretched film was inferior.

DESCRIPTION OF SYMBOLS 100 ... Film before extending | stretching 110 ... Center part 120 ... Both ends 130 ... Boundary part PA ... 1st thermoplastic resin PC ... 2nd thermoplastic resin 210 ... Feed block 220 ... T dice 230 ... Touch roll 240 ... Cooling roll 310 ... Clip 320 ... Drawing furnace

Claims (13)

After the thermoplastic resin is melt-extruded from the molding die, it is cooled and solidified by being taken up by a roll, and a pre-stretch film forming step for forming a pre-stretch film,
A stretching process for forming a stretched film by heating and stretching the pre-stretched film in at least one direction, and a method for producing a stretched film,
In the pre-stretching film forming step, the specific surface is obtained by planar extension in which a central portion of the pre-stretched film extends along a specific surface located near or in the middle of the thickness direction of the pre-stretched film. And the both ends of the pre-stretched film are contracted about the specific axis by uniaxial extension that is centered on the specific axis passing through the center of the both ends or near the center position. In the case where the minimum thickness of the boundary portion formed between the center portion and the both end portions is t _b and the average thickness of the center portion is t _c ,
The film before stretching is formed such that a ratio “t _b / t _c ” between the minimum thickness t _{b of the} boundary portion and the average thickness t _c of the central portion is 0.75 or more. A method for producing a stretched film. The method for producing a stretched film according to claim 1, wherein an acrylic resin is used as the thermoplastic resin. As the thermoplastic resin,
A first thermoplastic resin forming an inner region located on the inner side in the width direction of the pre-stretch film;
The stretched film according to claim 1, wherein an outer region located outside in the width direction of the pre-stretched film is formed and a second thermoplastic resin different from the first thermoplastic resin is used. Manufacturing method. The method for producing a stretched film according to claim 3, wherein an acrylic resin is used as the first thermoplastic resin. The stretched resin according to claim 4, wherein a mixed resin obtained by blending a thermoplastic resin having a glass transition temperature lower than that of the acrylic resin into polycarbonate (PC) is used as the second thermoplastic resin. A method for producing a film. The stretching according to any one of claims 3 to 5, wherein a thermoplastic resin having a glass transition temperature difference of 10 ° C or less is used as the first thermoplastic resin and the second thermoplastic resin. A method for producing a film. The maximum thickness of the end portions in the case of a _{t e,} the ratio between the average thickness _{t c} of the maximum thickness _{t e} of the end portions the central portion _"t e / _{t c"} is 1.0-2.0 The method for producing a stretched film according to any one of claims 1 to 6, wherein the pre-stretch film is formed in the pre-stretch film forming step so as to satisfy the following range. Wherein when the slit width of the outlet of the molding die was t _s, the ratio "t _{s /} t _c" of the average thickness t _c of the slit width t _s and the central portion of the outlet of the molding die, 8 The method for producing a stretched film according to any one of claims 1 to 7, wherein the pre-stretch film is formed in the pre-stretch film forming step so as to be 0.0 or less. The heat stretching of the pre-stretching film in the stretching step is performed by simultaneous biaxial stretching that simultaneously stretches in the length direction and the width direction of the pre-stretching film. A method for producing a stretched film. The method for producing a stretched film according to any one of claims 1 to 9, wherein a stretching ratio in a stretching direction of the heat stretching of the film before stretching in the stretching step is 3 times or less. 11. The heat stretching of the pre-stretched film in the stretching step is performed so that the thickness of the central portion of the stretched film after the heat stretching is in the range of 15 to 50 μm. The manufacturing method of the stretched film of description. The method for producing a stretched film according to any one of claims 1 to 11, further comprising a smoothing step of smoothing both side surfaces defining the thickness of the pre-stretched film before the stretching step. . The method for producing a stretched film according to claim 12, wherein the smoothing in the smoothing step is performed by removing regions located at both ends in the width direction of the unstretched film.

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